1. Field of the Invention
The present invention relates generally to an information recording medium with respect to which information can be optically recorded, erased, rewritten, and reproduced, and to a method of manufacturing the same.
2. Related Background Art
In a phase-change information recording medium, information is recorded, erased, and rewritten using a recording layer that is transformed in phase reversibly between a crystal phase and an amorphous phase. When this recording layer is irradiated with a high power laser beam and then is cooled rapidly, a portion thus irradiated is changed to be in an amorphous state and as a result, a recording mark is formed. Similarly, when an amorphous portion of the recording layer is irradiated with a low power laser beam and then is cooled slowly, the portion thus irradiated is changed to be in a crystal phase and as a result, a recording mark is erased. Therefore, in the phase-change information recording medium, the recording layer is irradiated with laser beams having powers modulated between a high power level and a low power level, so that new information can be rewritten while previous information is erased.
When information is to be rewritten, atoms move within the recording layer as the recording layer is transformed in phase between the crystal phase and the amorphous phase. As a result, in a conventional information recording medium, when rewriting is repeated, atoms may be concentrated locally to vary the thickness of the recording layer and this may cause deterioration in signal quality in some cases. Such repeated-rewriting performance is deteriorated particularly with the increase in recording density. The reason is that when the recording density increases, the intervals between adjacent recording marks are shortened and therefore the influence of the concentration of atoms in the adjacent recording marks increases.
In order to prevent the repeated-rewriting performance from being deteriorated, it is necessary to reduce the thickness of the recording layer to suppress the atom movement. In addition, the reduction in thickness of the recording layer also is a technique required to obtain a high density information recording medium with two recording layers. However, the reduction in thickness of the recording layer makes it difficult for atoms to move. Therefore, the crystallization rate of the recording layer decreases. The decrease in crystallization rate results in the deterioration in signal quality in a high density information recording medium in which small recording marks must be recorded in a short time. In addition, when the crystallization rate decreases, deterioration in crystallization sensitivity with time and that in erasing rate with time tend to occur. In other words, with the increase in recording density, it becomes difficult to achieve both the improvement in the repeated-rewriting performance and the suppression of the deterioration in crystallization sensitivity with time.
In order to improve the repeated-rewriting performance, a recording layer containing Te, Ge, Sn, and Sb has been reported (see JP 2(1990)-147289 A).
In the above-mentioned conventional recording layer, however, the crystallization rate was high but the repeated-rewriting performance and long-term reliability of the crystallization sensitivity in high density recording were not sufficiently high.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an information recording medium that allows high density recording to be carried out, is excellent in repeated-rewriting performance, and is deteriorated less in crystallization sensitivity with time, and to provide a method of manufacturing the same.
In order to achieve the above-mentioned object, an information recording medium of the present invention includes a substrate and a recording layer disposed above the substrate. The recording layer contains, as constituent elements, Ge, Sb, Te, Sn, and at least one element M selected from Ag, Al, Cr, Mn, and N. The term xe2x80x9cconstituent elementxe2x80x9d denotes an element indispensable for allowing a property of a material containing the element to be expressed. It is preferable that the recording layer consists essentially of Ge, Sb, Te, Sn, and at least one element M. The recording layer is transformed in phase reversibly between a crystal phase and an amorphous phase by an irradiation of energy beams. According to the information recording medium, it is possible to obtain an information recording medium that allows high density recording to be carried out, is excellent in the repeated-rewriting performance, and is deteriorated less in crystallization sensitivity with time.
In the above-mentioned information recording medium, the recording layer may be formed of a material expressed by a composition formula of
[(Ge, Sn)ASb2Te3+A]100xe2x88x92BMB,
where 0 less than Axe2x89xa610 and 0 less than Bxe2x89xa620. When Axe2x89xa610, the repeated-rewriting performance can be prevented from deteriorating. When Bxe2x89xa620, the deterioration in crystallization sensitivity with time can be prevented from worsening.
In the above-mentioned information recording medium, the content of Sn in the recording layer may be 2 atom. % to 20 atom. %. When the Sn content is set to be at least 2 atom. %, a sufficiently high crystallization rate can be obtained. In addition, when the Sn content is set to be not more than 20 atom. %, it is possible to increase the ratio of a quantity of reflected light when the recording layer is in a crystal phase to a quantity of reflected light when the recording layer is in an amorphous phase.
In the above-mentioned information recording medium, the recording layer may have a thickness of 5 nm to 15 nm. When the thickness of the recording layer is set to be at least 5 nm, the recording layer can be changed to be in a crystal phase easily. In addition, when the thickness of the recording layer is set to be not more than 15 nm, the repeated-rewriting performance can be prevented from deteriorating.
The information recording medium further may include a first protective layer, a second protective layer, and a reflective layer. The first protective layer, the recording layer, the second protective layer, and the reflective layer may be formed sequentially on the substrate. In this case, the information recording medium further may include an interface layer disposed in at least one position selected from a position between the first protective layer and the recording layer and a position between the second protective layer and the recording layer. Furthermore, the information recording medium further may include an optical absorption compensation layer disposed between the second protective layer and the reflective layer.
The information recording medium further may include a first protective layer, a second protective layer, and a reflective layer. The reflective layer, the second protective layer, the recording layer, and the first protective layer may be formed sequentially on the substrate. According to the above-mentioned configuration, an information recording medium can be obtained that allows particularly high density recording to be carried out. In this case, the information recording medium further may include an interface layer disposed in at least one position selected from a position between the first protective layer and the recording layer and a position between the second protective layer and the recording layer. Moreover, the information recording medium further may include an optical absorption compensation layer disposed between the reflective layer and the second protective layer.
A method of manufacturing an information recording medium according to the present invention is directed to a method of manufacturing an information recording medium provided with a substrate and a recording layer disposed above the substrate. The method includes forming the recording layer by a vapor deposition method. The recording layer contains, as constituent elements, Ge, Sb, Te, Sn, and at least one element M selected from Ag, Al, Cr, Mn, and N. The recording layer is transformed in phase reversibly between a crystal phase and an amorphous phase by an irradiation of energy beams. According to the manufacturing method, an information recording medium of the present invention can be manufactured easily.
In the above-mentioned manufacturing method, the vapor deposition method may be at least one method selected from a vacuum evaporation method, a sputtering method, an ion plating method, a chemical vapor deposition, and a molecular beam epitaxy.
In the above-mentioned manufacturing method, the vapor deposition method may be a sputtering method using a gas containing at least one gas selected from nitrogen gas and oxygen gas and one rare gas selected from argon and krypton.
In the manufacturing method, the recording layer may be deposited at a deposition rate of 0.5 nm/sec to 5 nm/sec. According to the configuration described above, a recording layer in the amorphous state can be deposited.
In the manufacturing method, the recording layer may have a thickness of 5 nm to 15 nm.